Power is generally supplied for a conventional communications device in two manners, namely, a centralized power supply manner and a fixed partition power supply manner. The centralized power supply manner is to supply power for a whole communications device by using a main power interface unit and a stand-by power interface unit. However, this power supply manner is merely applicable to a scenario in which power consumption of a communications device is relatively low, and if the power consumption of the communications device is relatively large, design of a power interface unit is complex, a size is large, and a cost is high. With an increase in power consumption of a communications device, a fixed partition power supply manner comes into being, where the communications device is divided into multiple different partitions, each partition corresponds to a fixed pair of a main power interface unit and a stand-by power interface unit, each partition may be plugged with multiple boards. However, when a new board is plugged, merely a main power interface unit corresponding to a partition in which the new plugged board is located can be used to supply power for the board. If there are a small number of boards plugged in each partition, in this case, power consumption of a communications device is relatively low, but all power interface units in each partition still need to supply power, which causes a waste of power interface units.